A dental ceramic can be colored e.g. by incorporating pigments into the ceramic material from the very beginning or using metal salts containing solutions which are applied on the surface of a porous dental ceramic article with the aim to color the dental ceramic article in its entirety. Coloring solutions are described in a couple of documents: WO 2004/110959 relates to a coloring solution for ceramic framework. The solution comprises a solvent (e.g. water), a metal salt and polyethylene glycol having a Mn in the range of 1.000 to 200.000.
WO 00/46168 A1 (corresponding to U.S. Pat. No. 6,709,694 B1) refers to coloring ceramics by way of ionic or complex-containing solutions containing defined concentrations of at least one salts or complexes of the rare earth elements or of the elements of the subgroups. The solution might contain additives like stabilizers, complex builders, pigments and beating additives.
WO 2008/098157 relates to a coloring solution for dental ceramic framework comprising a solvent, a coloring agent comprising metal ions, and a complexing agent, wherein the amount of complexing agent is sufficient to dissolve the coloring agent in the solvent.
WO 2009/014903 relates to a coloring solution for dental ceramic articles, the solution comprising a solvent and a coloring agent comprising rare earth element ions being present in the solution in an amount of at least about 0.05 mol/l solvent and transition ions being present in the solution in an amount of about 0.00001 to about 0.05 mol/l solvent.
In U.S. Patent Application Ser. No. 61/545,243 (3M IPC) aerogels, calcined and crystalline articles and methods of making the same are described. The content of this application is herewith incorporated by reference.
Sometimes, however, it is also desirable to use a whitening agent. Whitening agents are typically used to cover the metallic surface of a metallic dental framework in order to give the final dental restoration a more natural appearance. In certain cases, it can also be desirable to opacify e.g. the inner surface of a ceramic framework to cover discolorations of the tooth stump.
Compositions for whitening or opacifying dental metallic restorations are available in the market. Those compositions typically form a separate layer on the surface of the metallic framework and do not become part of the framework. These compositions often contain alumina as a whitening pigment to achieve the desired whitening effect. However, there is still room for improvement especially with regard to the requirements to be fulfilled with respect to modern dental materials. The present invention is intended to improve the known coloring and/or whitening processes.